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INTRODUCTION: Pharmacosomes are the colloidal dispersions of drugs covalently bound to lipids, and may exist as ultrafine vesicular, micellar, or hexagonal aggregates, depending on the chemical structure of drug-lipid complex. Pharmacosomes are amphiphilic phospholipid complexes of drugs bearing active hydrogen that bind to phospholipids. Pharmacosomes impart better biopharmaceutical properties to the drug, resulting in improved bioavailability. Pharmacosomes have been prepared for various non-steroidal anti-inflammatory drugs, proteins, cardiovascular and antineoplastic drugs. Developing the pharmacosomes of the drugs has been found to improve the absorption and minimize the gastrointestinal toxicity .

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APPLICATIONS: The approach has successfully improved the therapeutic performance of various drugs i.e. pindolol maleate, bupranolol hydrochloride, taxol, acyclovir, etc. The phase transition temperature of pharmacosomes in the vesicular and Micellar state could have significant influence on their interaction with membranes. Pharmacosomes can interact with bimembranes enabling a better transfer of active ingredient. This interaction leads to change in phase transition temperature of bimembranes thereby improving the membrane fluidity leading to enhance permeations.

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IMPORTANCE: Pharamcosomes have some importance in escaping the tedious steps of removing the free unentrapped drug from the formulation. Pharmacosomes provide an efficient method for delivery of drug directly to the site of infection, leading to reduction of drug toxicity with no adverse effects and also reduces the cost of therapy by improved bioavailability of medication, especially in case of poorly soluble drugs. Pharmacosomes are suitable for incorporating both hydrophilic and lipophilic drugs. Entrapment efficiency is not only high but predetermined, because drug itself in conjugation with lipids forms vesicles. There is no need of following the tedious, time-consuming step for removing the free, unentrapped drug from the formulation. Since the drug is covalently linked, loss due to leakage of drug, does not take place. No problem of drug incorporation Encaptured volume and drug-bilayer interactions do not influence entrapment efficiency, in case of pharmacosomes.

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In pharmacosomes, membrane fluidity depends upon the phase transition temperature of the drug lipid complex, but it does not affect release rate since the drug is covalently bound. The drug is released from pharmacosome by hydrolysis (including enzymatic). The physicochemical stability of the pharmacosome depends upon the physicochemical properties of the drug-lipid complex. Following absorption, their degradation velocity into active drug molecule depends to a great extent on the size and functional groups of drug molecule, the chain length of the lipids, and the spacer. They can be given orally, topically, extra-or intravascularly.

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PREPARATION: Two methods have been used to prepare vesicles: 1. The hand-shaking method 2. The ether-injection method In the hand-shaking method, the dried film of the drug–lipid complex (with or without egg lecithin) is deposited in a round-bottom flask and upon hydration with aqueous medium, readily gives a vesicular suspension. In the ether-injection method, an organic solution of the drug–lipid complex is injected slowly into the hot aqueous medium, wherein the vesicles are readily formed.

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FORMULATION OF PHARMACOSOMES: Drug salt was converted into the acid form to provide an active hydrogen site for complexation. Drug acid was prepared by acidification of an aqueous solution of drug salt, extraction into chloroform, and subsequent recrystallization. Drug -PC complex was prepared by associating drug acid with an equimolar concentration of PC. The equimolar concentration of PC and drug acid were placed in a 100-mL round bottom flask and dissolved in dichloromethane. The solvent was evaporated under vacuum at 40°C in a rotary vacuum evaporator. The pharmacosomes were collected as the dried residue and placed in a vacuum desiccator overnight and then subjected to characterization.

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EVALUATION OF PHARMACOSOMES: Pharmacosomes are evaluated for the following parameters. Solubility: To determine the change in solubility due to complexation, solubility of drug acid and drug-PC complex was determined in pH 6.8 phosphate buffer and n-octanol by the shake-flask method. Drug acid (50 mg) (and 50 mg equivalent in case of complex) was placed in a 100-mL conical flask. Phosphate buffer pH 6.8 (50 mL) was added and then stirred for 15 minutes. The suspension was then transferred to a 250 mL separating funnel with 50 mL n-octanol and was shaken well for 30 minutes. Then the separating funnel was kept still for about 30 minutes. Concentration of the drug was determined from the aqueous layer spectrophotometrically at 276 nm.

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Drug content: To determine the drug content in pharmacosomes of drug (e.g.: diclofenac-PC complex), a complex equivalent to 50 mg diclofenac was weighed and added into a volumetric flask with 100 mL of pH 6.8 phosphate buffer. Then the volumetric flask was stirred continuously for 24 h on a magnetic stirrer. At the end of 24 h, suitable dilutions were made and measured for the drug content at 276 nm UV spectrophotometrically. Scanning electron microscopy (SEM): To detect the surface morphology of the pharmacosomes, SEM of the complex was recorded on a scanning electron microscope.

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Differential scanning calorimetry (DSC ): Thermograms of drug acid, phosphatidylcholine (80 %) and the drug -PC complex were recorded using a 2910 Modulated Differential Scanning Calorimeter V4.4E (TA Instruments, USA). The thermal behavior was studied by heating 2.0 ± 0.2 mg of each individual sample in a covered sample pan under nitrogen gas flow. The investigations were carried out over the temperature range 25–250 °C at a heating rate of 10 °C min–1 . X-ray powder diffraction (XRPD): The crystalline state of drug in the different samples was evaluated using X-ray powder diffraction. Diffraction patterns were obtained on a Bruker Axs- D8 Discover Powder X-ray diffractometer, Germany. The X-ray generator was operated at 40 kV tube voltages and 40 mA tube current, using lines of copper as the radiation source. The scanning angle ranged from 1 to 60° of 2q in the step scan mode (step width 0.4° min–1). Drug acid, phosphatidylcholine 80 % (Lipoid S-80) and the prepared complex were analyzed.

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Dissolution study: In vitro dissolution studies of drug –PC complex as well as plain diclofenac acid were performed in triplicate in a USP (8) six station dissolution test apparatus, type II (Veego Model No. 6 DR, India) at 100 rpm and at 37 °C. An accurately weighed amount of the complex equivalent to 100 mg of drug acid was put into 900 mL of pH 6.8 phosphate buffer. Samples (3 mL each) of dissolution fluid were withdrawn at different intervals and replaced with an equal volume of fresh medium to maintain sink conditions. Withdrawn samples were filtered (through a 0.45-mm membrane filter), diluted suitably and then analyzed spectrophotometrically at 276 nm.

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CONCLUSION: Vesicular systems have been realized as extremely useful carrier systems in various scientific domains. Over the years, vesicular systems have been investigated as a major drug delivery system, due to their flexibility to be tailored for varied desirable purposes. In spite of certain drawbacks, the vesicular delivery systems still play an important role in the selective targeting, and the controlled delivery of various drugs. Researchers all over the world continue to put in their efforts in improving the vesicular system by making them steady in nature, in order to prevent leaching of contents, oxidation, and their uptake by natural defense mechanisms.